High dielectric material



Patented Oct. 25, 1948 HIGH DIELECTRIC MATERIAL Eugene Wainer, NiagaraFalls, N. Y., assignor to The Titanium Alloy Manufacturing Company, NewYork, N. Y., a corporation of Maine No Drawing. Application November 2.1943,

Serial No. 508,744

I 8 Claims. (01. 106-39) This invention relates to ceramic dielectricmaterials, More particularly, it relates to such materials in whichcompounds of titanium are the predominating constituent used incombination with compounds of zirconium and tin.

In previous applications for patent, namely, Serial No. 482,613 filedApril 10, 1943, now Patent No. 2,420,692 of May 20, 1947; Serial No.489,382 filed June 2, 1943, now Patent No. 2,377,910 of June 12, 1945;Serial No. 490,485 filed June 11, 1943, now Patent No. 2,402,515 of June18, 1946, and Serial No. 377,851 filed February 7, 1941, now Patent No.2,371,660 of March 20, 1945, the useful properties of mixtures ofalkaline earth titanates, of certain titanates and fluorides, oftitanates and stannates and of titanium with certain metal oxides havebeen described and claimed, The present invention relates to anothergroup of bodies prepared by compounding titanates ceramically withzirconates and stannates whose usefulness is equally widespread. Thisnovel group of ceramic compositions have properties such as to make themuseful as capacitors in radio, television, and communications generally,as capacitative temperature compensating devices in receivers andcommunication equipment to prevent distortions due to changes in circuitcharacteristics caused by temperature changes.

The dielectric constants of some of these compositions are so high as tomake possible their utilization in low frequency distribution andcommunication systems such as 60 cycle lines, by means of capacitativecoupling between a low frequency high tension transmission line andcommunication telephone lines. Further, these high constants enablethose materials to be used as substitutes for high capacity paper andelectrolytic type condensers for by-pass, filter, and power circuits,for use in radio, fluorescent lighting circuits, etc.

Further, the very high dielectric constants make possible the use ofthese materials as electro-mechanical devices, for example, the transferof mechanical energy or motion into electrical energy or vice versa, ina fashion similar to the action exhibited by piezoelectric crystals.Thus the novel compositions of .the present invention have possibleutility in pyroelectricity, supersonics, crystal or condensermicroph'oneairequency stabilizers, loud speakers, phonograph pick ups,telephone design, and oscillator designs generally. The foregoingremarks apply particularly to those bodies whose dielectric constantsare over 1000 at radio frequency. In condenser microphones, very thinsheets of the higher dielectric constant materials are rigidly clampedat either center or edges and used as vibrating diaphragms. The minutechanges of dimension or position of the dielectric due to vibration willoccasion relatively large changes 'in capacity by means of which soundis transformed .into electrical energy.

Other members of this group; particularly those having dielectricconstants over 1000 appear to exhibit electrical and mechanicalcharacteristics of the same nature as piezoelectrical and pyroelectricalcrystals, For example, a rod of the material having one .end fixed andone end free to vibrate will develop a potential difierence of severalvolts between the two ends of the rod, when in vibration. The particularusefulness of this group as compensators for correction of frequencydrift lies not only in the possibility of obtention of both positive andnegative temperature coefficients of a wide variety but also thepossibility of controlling the variation through choice of the propercomposition. Furthermore, some of the temperature coefficients makemembers of the group useful as mica substitutes, particularly because ofthe low power factors available.

These novel compositions consist broadly of fired mixtures of thetitanates ofthe alkaline earths, particularly barium titanates, with thezirconates and stannates of the alkaline earths. The alkaline earthcompounds generally are of utility for this invention, including thoseof magnesium, calcium, strontium and barium. The

peculiarly beneficial efiect of the zirconatestannate additions is moststrikingly shown in the case of additions to BaTiOa. At radiofrequencies barium titanate has a dielectric constant of 1200-1300, anda temperature coefficient which is first negative, then stronglypositive, and finally strongly negative between 20 and C. Not on y maythis erratic behavior be eliminated by addition of the zirconates andstannates to barium titanate but dielectric constants of the order ofseveral thousand are common.

In the practice of the present invention, the ingredients as indicatedin the table below are properly reacted ceramically and then ground sothat the coarsest particles will pass a 325 mesh screen. The driedpowders are then mixed within the limits indicated by the proportionsgiven in the table. Approximately 10% water is added and thoroughlymixed in the damp powder, granulated by passage through a 20 meshscreen. They are then pressed in a die under a pressure of 5 to 10 tonsper square inch, and then allowed to air dry for 24 hours. The piecesused for the purposes of this specification are roughly 1 inch indiameter and 0.1 inch thick. Pieces of such size are flred on a scheduleof 400 F. per hour to the peak temperature, then held at peaktemperature for three hours, and then allowed to cool. The maturationtemperature for all the bodies listed below is between 2450 F. and 25110F. After cooling, the opposing parallel surfaces are painted with silverpowder paste which is fixed as a silver electrode by firing to 1500 F.

The values obtained below were determined at one megacy-cle, using aradio frequency bridge of standard design. Resistivity was determined ona high sensitivity resistance circuit on which a resistance'of a millionmegohms could easily be detected, the zero point indicator being agalvanometer. The 1000 cycle measurements were ob-. tained through useof an impedance bridge of standard design, whose arms were resistivecomponents.

The data below indicate that not only may these groups of compositionsbe used for by-pass, filter, and power pack condensers as substitutesfor paper and eiectrolytics but also as substitutes for mica both fromstandpoint of power factor and temperature coemcient. The possibility ofvariation and control of temperature coemcients is indicated from Table2. These data were ohrials which, as a group, exhibit an almost flattemperature variation of capacity over a range of nearly 60 C. They thuscover the complete range of household temperatures. The last threecompositions are smoothly negative and exhibit the flattest temperaturecurves of a positive-neutralnegative type of any series investigatedthus far. Furthermore, such temperature characteristics are availablewith the highest dielectric constant yet developed for this type oftemperature variant dielectric.

From the foregoing, it will be seen that the stanna-tes, titanates andzirconates oi the alkaline earth metals including magnesium can becombined ceramically to provide useful dielectric materials wherein thedielectric contains two or more of these chemicals. All of thesesubstances have the same crystal lattice structure as the calciumtitanate mineral perovskite, namely, a face centered body centered cube.The invention is, therefore, directed to ceramic mixture of two or moresubstances having the perovskite structure.

What is claimed is:

1. A dielectric composition comprising an alkaline earth titanate, analkaline earth stannate and and an alkaline earth zirconate.

2. A dielectric composition comprising an alkaline earth 'tit-anate, analkaline earth stannate and tained at one megacycle. magnesiumzirconate.

One Megacyclc One Kiloeycie Comp. Parts by weight of Tltmate zkemmteDielectric Power Dielectric Power Constant Factor Constant Factor Percent Per cent 3, 950 2. 85 5. 050 3. 73 4, 300 3. 70 BaSnOz-i-S BaZr0;4, 050 3. 36 BaSnOa-H 1382103. 3, l90 1.61 BaQnOz-HO BaZrO; 3,310 l. 04100 B3Ti0;+i BaSn01+3 MgZi'Oz. 3, 010 1. 57 100 BaTio -i-a BaSnOs-l-BMgZrOa- 3, 000 1. 40 100 BnTiOrf-5 .770 1. 73 2. 860 1.62 3, 010 1. 343.080 0. 96 500 0. 76 2, 250 0. 71

Tun.- 2 Temperature coeflicicnt of capacity Body B dy Body Body BodyBody B dy Body Body Body Body 139 #40141 1431441 #40 #47#48#49 Thetemperature coefllcients of the composi- 3. A dielectric compositioncomprising an alkations listed are indicative of the scope of varia--tion possible. While single compositions may yield the desiredcoeflicient, an infinite variety of coeificient is possible throughparallel combination of one or more bodies.

The special characteristics of the titanate, stannate, zircona-tecompositions are as follows, the relatively low stannate-magnesiumzirconate adline earth titanate, barium stannate and magnesiumzirconate.

4. A dielectric composition comprising barium titanate, barium stannateand magnesium zirconate.

5. A dielectric composition comprising barium titanate in major amountand an alkaline earth 5 stannate and an alkaline earth zirconate inminor amount.

6. A dielectric composition comprising barium titanate in major amountand barium stannate and an alkaline earth zirconate in minor amount.

7. A dielectric composition comprising barium titanate in major amountand barium stannate and magnesium zirconate in minor amount.

8. A dielectric composition comprising the titanate, stannate andzirconate of barium.

EUGENE WAINER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Soyck Feb. 9, 193':

Number and Theoretical Chemistry, vol. 7, pages 52, 53, 54, 94, 136, 418and 419 (1927).

Danas Textbook of Mineralogy, 4th ed. (1932) pages 26, 2'7, 28, 692 and693.

